This invention is in the field of seismic prospecting, and is more specifically directed to the automated extraction of signals indicative of faults from seismic survey signals.
As is fundamental in the field of geology, particularly as applied to the prospecting for oil and gas, faults are surfaces within the earth's crust at which sedimentary layers and other geological features are disrupted, so as to be no longer smoothly continuous. As is well understood in the field, faults can form effective barriers to subsurface hydrocarbon flow, causing oil and gas to accumulate at faults in some cases. Accordingly, the detection and characterization of faults is an important tool in the search for oil and gas reserves, and the accuracy with which such faults can be detected and characterized can have significant impact in identifying and exploiting these reserves.
Seismic prospecting techniques are a fundamental tool in modern oil and gas prospecting, as these techniques provide efficient generation of subsurface surveys over a relatively wide region of the earth, in both land-based and marine contexts. With the advent of improved signal gathering and analysis technologies, three-dimensional ("3-D") seismic surveys are now commonly generated from seismic survey signals, permitting the analyst to more accurately visualize and characterize apparent subsurface discontinuities.
As noted above, faults are important subsurface features that are often of interest to the geologist. According to conventional techniques, the identification of faults in coherent 3-D seismic volumes is typically performed by human analysts, through manual identification and interpretation (i.e., "picking") of potential faults from seismic amplitude data. Of course, manual fault picking is an extremely time consuming process, and is thus quite costly. Additionally, manual interpretation is to a large extent dependent upon the skill, experience, and subjectivity of the individual analyst, resulting in imprecise results.
By way of further background, the automated calculation of correlation or coherency values from 3-D seismic amplitude data is known in the art. According to this approach, an example of which is described in U.S. Pat. No. 5,563,949, geologic discontinuities such as faults are directly imaged from non-correlation or non-coherency events in the 3-D seismic volume. However, this approach and other conventional methods do not provide any sort of automatic or quantitative interpretation of faults, but instead simply image the location of discontinuities in the dataset.
By way of still further background, the elimination of horizontal stripe artifacts from satellite images of the surface of the earth is known, as described in Mather, P. M., Computer Processing of Remotely-Sensed Images (John Wiley & Sons, 1987).
By way of still further background, techniques for extracting ridge and valley lines from digital terrain models are known in the art Examples of these techniques are described in Riazanoff et al., "Ridge and valley line extraction from digital terrain models", Int. J. Remote Sensing, Vol. 9, No. 6 (1988), pp. 1175-83.